Computer scientists in the US have discovered ways to “re-identify” the names of people included in supposedly anonymous datasets.

In one example, a movie rental company released an anonymous list of film-ratings taken from its 500,000 subscribers. Using a statistical “de-anonymisation” technique, the academics were able to identify individuals and their film preferences.

The discovery raises concerns about how safe it is to release personal information – such as medical records or mobile phone data – even if details such as names or national insurance numbers have been removed. There are fears the information could be accessed by criminals.

The discovery has led British researchers to raise the issue in a report they are writing for the European commission. Dr Ian Brown, of the Oxford Internet Institute and a co-author, said the example of the film list was relatively trivial. “But this raises concerns for more sensitive data such as medical records. Epidemiologists say they could do interesting research if they had access to more anonymous data. This shows it is difficult to do that in a way that can’t be reversed.”